Betting calculators
Six calculators that run entirely in your browser. Each one shows the formula it uses, because a calculator you cannot check is just a number with a font.
The six
Nothing here calls a server, stores an input or loads a third-party script. Type a number, read the answer, check the formula.
Odds Converter
American, decimal, fractional and implied probability. Enter any one format, get the other three.
Implied Probability
Turn a price into the win rate you need to break even, and the win rate you need to hit a target return.
Vig & Hold Calculator
Two-way or three-way market in, total margin and the no-vig fair line for every side out.
Expected Value Calculator
Stake, price and your probability estimate in; EV per bet, EV as a share of stake and a long-run projection out.
Parlay Calculator
Two to twelve legs. What the book pays against the devigged fair price, and how the margin compounds.
Bankroll & Kelly Staking
Full, half and quarter Kelly against a flat stake, with the growth-rate maths that explains why overbetting is fatal.
How to use these together
The calculators chain in a sensible order. Start with the odds converter to get every price into the same units. Run the market through the vig calculator to strip out the operator's margin and see the fair line rather than the posted one. Compare that fair line to your own estimate in the EV calculator. If there is something there, size it with Kelly, then take the fraction of Kelly your confidence in the estimate actually justifies.
The implied probability page answers the question people usually mean when they ask whether a price is any good: what would you have to hit for this to be worth it? The parlay calculator exists mainly to make one thing visible, which is that combining bets multiplies the margin as well as the price.
All six share one limitation. They are exact about arithmetic and silent about judgement. Every output that depends on a probability you supplied is a restatement of that estimate, not evidence for it.